OPUS 4 | Geowissenschaften

The Aptian evolution of the Galve sub-basin (Maestrat Basin; E Iberia) (2010)

Telm Bover-Arnal

The epeiric mixed carbonate-siliciclastic sedimentary succession of Aptian stage (125-112 Ma) cropping out in the Galve sub-basin (western Maestrat Basin) in the eastern Iberian Chain (E Iberia) was analyzed by multiscale and multidisciplinary approaches. The integrated basin analysis presented in this thesis highlights the interplay between the solid Earth, oceans, atmosphere and life during this time interval, marked by higher CO2 atmospheric concentrations than nowadays and, consequently, by extreme climatic warmth and higher global sea levels. The most noteworthy aspect of this sedimentary succession is that its analysis enables all major ocean-climate changes which occurred during this stage to be tracked, and it therefore constitutes an excellent means of measuring this time slice. The Aptian strata studied can be divided into four large-scale transgressive-regressive sequences, which were calibrated by geomagnetic polarity analysis and ammonoid and rudist biostratigraphic data. These sequences are consistent with the major transgressions and sea level falls recorded in other coeval Tethyan localities, indicating a significant eustatic control of the sedimentary succession, although synrift subsidence was the most important mechanism in providing accommodation. The main oceanographic and climate-driven Tethyan events detected were: 1) An Early Aptian transgressive phase accompanied by the widespread development of Palorbitolina lenticularis beds. 2) The δ13C perturbations related to the OAE1a have been localized in the upper part of the Deshayesites forbesi biozone within a horizon of coral rubble deposits encrusted by Lithocodium aggregatum and Bacinella irregularis, coincident with the probable Early Aptian thermal maximum. These encrusted coral rubble levels with widespread presence of large-sized flattened Palorbitolina lenticularis are interpreted here as records of physical and chemical disturbances linked to the OAE1a. 3) A late Early Aptian long-term progressive cooling trend accompanied by a regressive context marked by the establishment of large carbonate platforms with typical Urgonian biotic associations dominated by rudist bivalves and corals. 4) The maximum of the aforementioned regressive phase, which exposed subaerially the carbonate platform formed during the late Early Aptian. As a result, a broad palaeokarst developed in its proximal setting, whilst forced regressive wedges were deposited basinwards. This late Early Aptian stratigraphic interval constitutes a text-book example of the application of the four-systems-tract sequence stratigraphic methodology to carbonate systems. 5) A late Early to Late Aptian long-term regressive context, which gave rise to the establishment of littoral conditions during the Late Aptian. The installation of more proximal conditions in this area was coupled with significant terrigenous supplies, which were probably linked to regional tectonics and to a progressively changing climate from a semi-arid regime during the Early Aptian, to semi-humid conditions in the Middle-Late Aptian. Consequently, this study represents a well-documented example of the evolution of the Aptian epicontinental seas, and hence constitutes a valuable tool for calibrating analyses of other Aptian epeiric sedimentary successions.

The effect of iron on the stability, water content and compressibility of mantle silicates – Implications for a hydrous Martian interior (2010)

Geertje Ganskow

Summary This thesis addresses three different effects of Fe on the properties of nominally anhydrous transition minerals and dense hydrous Mg-silicates. Furthermore, the potential presence of dense hydrous Mg-Fe silicates (DHMS) in the Martian interior and the water storage potential of a hydrous Martian mantle are evaluated. 1. The effect of iron on the water content of ringwoodite The results show that the water contents of Fe-rich ringwoodites of about 0.4-0.7 wt% H2O are considerably reduced compared to pure Mg-ringwoodite. Thus, the ringwoodite samples show an inverse correlation of Fe- and water content. The Mg-site octahedra represent the favored protonation site in ferroan ringwoodites corresponding to the Mg2+=2H+ water substitution mechanism. In addition, Fe3+ diminishes the water content of ringwoodites due to the reduction of potential protonation sites. This is caused by the creation of Mg-site vacancies by the oxidation of Fe and the occupation of octahedral sites by Fe-atoms, which are probably not involved in water substitution mechanism. These results indicate that less water can be stored in nominally anhydrous mantle silicates of Fe-rich planetary mantles. 2. The effect of iron on the compressibility of hydrous ferroan ringwoodite The effect of Fe on the compressibility of ringwoodite is particularly important for the interpretation of the structure of Fe-rich planetary interiors such as the Martian mantle. Measurements at ambient conditions yield to unit-cell lattice parameters of a=8.1597(6) Å and V=543.28(13) Å³ (run 3854) and a=8.1384(3) Å and V=539.03(7) Å³ (run 4218). The P-V data were fitted with a second-order Birch-Murnaghan equation of state. The first pressure derivative of the bulk modulus, K´, was fixed to the value of 4 yielding to the following refined equation of state parameters: V0=543.32(7) Å³ and KT0=186.5(9) GPa (run 3854) and V0=539.01(5) Å³ and KT0=184.1(7) GPa (run 4218). Structural refinements indicate significant octahedral vacancies in sample 4218 due to the presence of 0.1 Fe3+ a.p.f.u. and the substitution of ~0.37 wt% H2O. The values of bulk modulus of (Mg,Fe)2SiO4-ringwoodites found in this study are very similar to that of the Fe-endmember ringwoodite, which suggests that the Fe substitution has little effect on the compressibility of ringwoodite. This also indicates that the close-packing of oxygens of the spinel structure is the major factor in determining its compressibility. This cannot be affected by the presence of up to 0.1 a.p.f.u. of vacancies. 3. The effect of iron on the stability of hydrous mantle silicates The transformation pressure of olivine to wadsleyite (simple Martian mantle composition) is lowered by 2 GPa. The shifts of stability fields toward lower pressures are possibly caused by the presence of Fe3+ and H2O. The shift of the olivine-wadsleyite transition would result in an extended upper mantle transition zone, compared to the anhydrous mantle, and consequently yield an increased water storage potential of the Martian mantle. The DHMS, phase D and superhydrous B (SHyB) show stabilities up to 1300°C at 23 GPa (phase D, MgFeSiO4+9.5 wt% H2O bulk composition) and for the simple Martian mantle composition up to 1450°C at 20.5 GPa (phase D and SHyB), which represents a higher stability of DHMS than previously reported. This suggests that phase D and SHyB are relevant DHMS in Fe-rich mantles of planetary systems. 4. The potential presence of dense hydrous Mg-Fe silicates in the Martian interior and the water storage potential of a hydrous Martian mantle This experimental study of mantle silicates indicates that the Martian mantle consists basically of upper mantle with olivine, garnet and pyroxene, as well as upper and lower transition zone build up by wadsleyite and ringwoodite together with pyroxene and majoritic-garnet, respectively. The water contents of wadsleyite with 0.6 wt% H2O and ringwoodite with 1.1 wt% H2O are reduced compared to the Mg-endmembers. The Martian transition zone, however, shows the largest water storage capacity since the upper mantle mineral olivine accommodates up to 0.3 wt% H2O. Pressure and temperature conditions at the core-mantle boundary are insufficient to reach the perovskite stability field, i.e. a lower Martian mantle cannot be expected based on the results of this study. These results imply that significant amounts of water can be stored in the Martian transition zone as well as the upper mantle. In addition, DHMS would be stable up to 1450°C at 20.5 GPa in a hydrous Martian mantle model. On the basis of thermal evolution models of the Martian mantle, and Fe partitioning data between mineral phases and melt it is discussed that DHMS may form in the Martian interior at P-T conditions corresponding to the lower Martian transition zone.

Investigation of the properties of iron-bearing alloys and silicates and their implications for the Earth’s lower mantle and core (2010)

Olga Narygina

(1) (Mg,Fe)(Si,Al)O3 perovskite comprises about 80% of the Earth’s lower mantle by volume, leaving ~ 15% to (Mg,Fe)O ferropericlase and ~ 5% to CaSiO3 perovskite. Therefore characteristics of the lower mantle would be determined mostly by the properties of the silicate perovskite and ferropericlase. While high-spin – low-spin crossover in (Mg,Fe)O is nicely described in literature, the electronic state of iron in silicate perovskite at high pressures and temperatures remains controversial. Conclusions derived from the results of X-ray emission (XES) and nuclear forward scattering (NFS) spectroscopic studies of Fe-bearing silicate perovskite are not in agreement on the pressure and temperature conditions of the transition and on whether Fe2+ or Fe3+ or both iron cations are involved. We undertook an alternative study of (Mg,Fe)(Si,Al)O3 perovskite at a wide pressure and temperature range using a number of different spectroscopic techniques (conventional Mössbauer, X-ray absorption near edge structure (XANES), NFS and X-ray diffraction (XRD) spectroscopies), in order to get a rather complete picture regarding the spin state of iron in this compound. Desirable pressures relevant to those in the Earth’s lower mantle were achieved by means of diamond anvil cells, equipped with miniature external resistive heaters, providing homogeneous heating up to 1000 K, which enables us to estimate the effect of temperature as well. Our Mössbauer and XANES data, collected at pressures to 110 GPa and temperatures to 1000 K for silicate perovskite, revealed a gradual transition involving Fe2+, which at room temperature occurs over a rather wide pressure range, 35-70 GPa, but becomes narrow at high temperatures. This observation coincides with the previously reported drop in spin number revealed by XES. Taking this into account and based on the fact that our XRD measurements, performed at the corresponding pressure-temperature conditions, do not suggest any appreciable structural change in perovskite, we conclude that the origin of the observed transition is fully electronic. Considering the simplified energy diagram of ferrous iron, sitting in 8-12 fold coordinated polyhedra in the perovskite structure, and by analysing the effect of pressure on the distribution of valence electrons over the energy levels, we propose stabilization of intermediate spin Fe2+ in magnesium silicate perovskite at pressures over 35 GPa. The gradual character of high-spin – intermediate-spin crossover in silicate perovskite does not assume any abrupt changes of the lower mantle properties. However due to the negative Clapeyron slope of the transition in some areas in the uppermost lower mantle, located in the vicinity of subducting slabs or hot mantle upwellings, they would have slightly different properties (namely electrical and thermal conductivity, element partitioning) with respect to the surrounding mantle. (2) Although the effect of spin transitions in lower mantle silicate perovskite and ferropericlase on the iron partitioning between these two phases has been widely discussed in the literature, the question remains open, mainly due to the lack of in situ experiments under the relevant pressure and temperature conditions. We approach this problem using combined in situ synchrotron XRD and XANES spectroscopic measurements with laser-heated diamond anvil cell (LH-DAC) technique. The assemblages of perovskite and ferropericlase were synthesized via the breakdown reaction of ringwoodite or a natural San Carlos olivine. Our data, collected from 22 GPa to 115 GPa, after laser heating to 1950 K and 2300 K, confirmed previously reported preferred partitioning of iron in low-spin ferropericlase with respect to high or intermediate spin perovskite. Increase of temperature was shown to slightly increase the amount of Fe in perovskite. (3) The phase diagram of Fe-enriched FeNi alloy at elevated pressures and temperatures comparable to those in the Earth’s core as well as the effect of the potential light element in the core on the system remains under debate. The reason is very simple: the necessary pressure-temperature range (300-350 GPa and 5,000-7,000 K) is hardly achieved in the laboratory. Conditions close to those in the core can be created in LH-DAC experiments; however the main disadvantage of the technique is a lack of control on the system under study. In contrast, the large-volume press (LVP) provides rather equilibrated and controllable experimental conditions, although at significantly lower pressures. Therefore we carried out a “cross-checking” study of phase relations in Fe1-xNix (0.10 < x < 0.22) and Fe0.90Ni(0.10-x)Cx (0.01 < x < 0.05) systems at pressures to 52 GPa and temperatures to 2600 K, using LH-DAC and LVP high pressure techniques. In situ and ex situ sample analyses were done by means of XRD, Mössbauer spectroscopy, and scanning and transmission electron microscopies. We showed that laser heating in the DAC can promote undesired reactions between the sample (FeNi alloy in our case) and carbon, which upon laser heating diffuses from the diamond anvils through the pressure-transmitting layers. We investigated the mechanism of carbon incorporation into the structure of FeNi alloy at high pressures and temperatures, and showed that rapid cooling of fcc-structured carbon-bearing FeNi alloy to room temperature (either in the case of LH-DAC or LVP quenched experiments) results in the formation of the metastable solid solution of bcc-FeNi, bct-Fe-Ni-C (known in metallurgy as martensite) and a certain amount of preserved fcc Fe-Ni-C.

Improved Intermittent Clutter Filtering For Wind Profiler Radar (2010)

Volker Lehmann

Ground-based remote measurements of the vertical profile of the horizontal wind vector in the atmosphere by radar wind profiler (RWP) is a technique that has been significantly developed since the first demonstration with the Jicamarca radar by Woodman and Guillen in the early 1970s. Currently, there exist several operational networks of those instruments in the USA, Europe and Japan which provide continuous wind measurements in real-time and most of the data are successfully assimilated in numerical weather prediction models. Although this is an obvious indication of maturity, practical experience has shown that further improvements are both possible and necessary. While the high sensitivity of these clear-air radars is required for receiving the weak atmospheric echoes, it makes them also particularly vulnerable to unwanted radar returns and in-band radio frequency interference. Signal processing must therefore especially deal with the problem of filtering of these unwanted contributions, to avoid associated measurement errors. A specific difficulty are clutter echoes from various airborne objects, such as aircraft or birds, which generate strong, intermittent contributions to the received signal. The standard RWP signal processing is not able to deal with these signals in an efficient way, because the model assumption on which the processing is based is violated. With the development of sophisticated mathematical tools for the analysis of non-stationary signals in the last two decades and a better understanding of the practically relevant RWP clutter issues, a number of efforts have been made to tackle especially the challenging problem of intermittent clutter returns from migrating birds. In this dissertation it is shown that the signal structure of RWP raw data contaminated by intermittent clutter is much clearer revealed by a joint time-frequency analysis based on the windowed Fourier transform than by other possible signal descriptions, in particular pure time or frequency representations. An effective intermittent clutter reduction algorithm, called the Gabor filter, is obtained by a combination of a numerically feasible discrete Gabor frame expansion with the statistical test for a stationary Gaussian random signal. This approach is optimized by using near-tight frames and selecting a time-frequency resolution that provides a jointly sparse representation of both atmospheric and clutter signal components. A first evaluation of this approach has shown a superior performance in comparison with hitherto existing methods, but it was also found that additional quality-control of the derived Doppler spectra is still required during extreme bird migration events. The latter is in all likelihood indicative of a principal limit of radar wind profiling during such conditions. However, an effective quality control of the measurement is possible through a combination of a stationarity estimate provided by the Gabor algorithm with a-priori information about typical atmospheric echoes.

Die Berücksichtigung inhaltlicher und räumlicher Unschärfe bei der GIS-gestützten Erstellung von Bodenkarten (2010)

Jens Hannemann

Die vorliegende Arbeit beinhaltet die Entwicklung einer Methode zur objektivierten Erzeugung von Flächendaten für Bodenkarten. Ziel ist es, Daten, die sich in Maßstab, Datum, Art, Herkunft und Güte unterscheiden, zu bewerten, zu verknüpfen und unter Berücksichtigung ihres Raumbezuges zu einem Zielthema zusammenzuführen. Es werden zunächst der informationstheoretische Hintergrund, sowie bestehende Regionalisierungsverfahren und -ansätze betrachtet. Eine wichtige Rolle spielt die Auseinandersetzung mit dem Sequenz- und Vergesellschaftungsprinzip, sowie der Maßstabsproblematik. Es wird ausführlich auf die vorhandenen Informations-grundlagen eingegangen. Ausgangspunkt ist, sämtliche zur Verfügung stehenden Datenbestände in die Analyse zu integrieren. Die Beschreibung und das Aufzeigen von Analyse- und Bewertungsmöglichkeiten dieser sehr heterogenen Daten nimmt dabei einen zentralen Platz ein. Eine wichtige Rolle spielt stets die Interaktion von Computer und Experten. Die Methode durchläuft die Kette Aufbereitung, Verarbeitung, Auswertung und Visualisierung bodenkundlicher Informationen. Als Bausteine werden bekannte, aber auch neu entwickelte Methoden verwendet, diskutiert und kombiniert. Die Entwicklung der Gesamtmethode bzw. des methodischen Ablaufs an sich steht dabei im Vordergrund. Hauptziel ist die Ausweisung von Kern- und Übergangsbereichen. Es wird besonderer Wert darauf gelegt, die intrinsischen Unterschiede in den Daten herauszuarbeiten und während des gesamten Methodenablaufs mitzuführen. Dazu wird konsequent das Abstufungsprinzip für die inhaltliche und räumliche Komponente gleichermaßen angewendet. Der Umgang mit der inhaltlichen und räumlichen Unschärfe bildet den Schwerpunkt der Arbeit. Es werden Zielkategorien definiert, die die Bewertungs-grundlage für die räumlich auszuweisenden Bodenformen darstellen. Der gesamte Methodenablauf ist eingebettet in die fuzzy-logischen Arbeitsschritte Fuzzifizierung, Inferenz und Defuzzifizierung. Es wird ein Ansatz vorgestellt, der die Verarbeitung unscharfer bodenkundlicher Informationen zu optimieren versucht. Durch eine gewichtete, inhaltlich-räumliche In-Beziehung-Setzung von Daten, durch eine Analyse von qualitativen und quantitativen Daten und die Einbeziehung sprachlicher Modifikatoren wird eine Konzeptkarte mit objektivierter Arealabgrenzung erarbeitet, die auf einer reproduzierbaren Datenverarbeitung und einer quantifizierten Aussagesicherheit fußt. Datenbank, GIS und Bildverarbeitung bilden dabei softwareseitig die Hauptkomponenten. Zur Ergebnis führenden Ausweisung der Kern- und Übergangsbereiche wurde die Bildverarbeitungsmethode der Segmentierung gewählt. Diese wurde mit der Software eCognition vorgenommen. Inhalt und Abgrenzung der Segmente wurden mit den Punktdaten eines Transektes von der Hochfläche über die Niederung zur Hochfläche überprüft. Im Zusammenhang mit der Darstellung der Aussagesicherheit in Karten wird das Prinzip der Raumübertragung und Übertragungsgütemaße aufgegriffen und diskutiert. Es wird ein Zwei-Karten-Konzept angeregt, das neben der Karte mit der eigentlichen Fachinformation stets eine Karte der Aussagesicherheit vorsieht. Weiterhin wird auf Aspekte der Visualisierung der inhaltlichen und/oder räumlichen Komponente eingegangen. Ziel ist dabei die synoptische Darstellung von Infor-mationsergebnissen für den Nutzer.

The 5-th element. A new high pressure high temperature allotrope (2010)

Evgeniya Zarechnaya

Boron is the fifth element in the Periodic Table known for its structural complexity, unusual types of bonding, and for a rich variety of compounds that it forms. Even the number of its existing or hitherto proven elemental modifications is still under discussion. The present study of boron behavior at high pressures and high temperatures (HPHT) comprises various experimental techniques for HP synthesis and material characterization, as well as theoretical modeling. A series of high pressure (up to 20 GPa) and high temperature (up to 1900 °C) synthesis experiments were conducted in multianvil apparatus at Bayerisches Geoinstitut. For testing of the reproducibility of HPHT experiments different types of boron precursors and assemblages for large-volume presses were used. The synthesis products were studied by X-ray diffraction and spectroscopic methods. The diffraction patterns collected from samples synthesized from highly purified boron powders (> 99.99 % purity) resemble those published by R.H. Wentorf in 1965 and described as a new boron form, but later effectively forgotten. To eliminate any possible contaminations that could take place during the synthesis process, the purity of the HP boron samples was confirmed by scanning electron and transmission electron microscopy and electron microprobe analysis. The structure of this HPHT boron polymorph was first unknown, but subsequently determined from our X-ray powder diffraction data and further refined using single-crystal synchrotron diffraction data. The structure was found to be orthorhombic with a Pnnm space group and composed of B12 icosahedra and B2 dumbbells. The unit cell contains 28 atoms (two icosahedra and two dumbbells) and will be called here B28. Atoms in B28 are bonded covalently as revealed experimentally by single-crystal X-ray diffraction studies and calculated Electron Localization Function. The X-ray density of 2.52 g cm-3 of this boron allotrope is the highest among its other known modifications. In order to determine the phase transition boundary between beta-and B28 boron phases, in situ HP laser heating experiments were performed at European Synchrotron Radiation Facilities (ESRF). It was demonstrated that B28 is a stable phase above 9 GPa. Systematic investigations aimed at the development of the technique of the HP single crystal growth of B28 were undertaken. It was found that single crystals of the orthorhombic boron can be grown from metal solutions (Au, Cu, or Pt), i.e. after dissolution in metals at high temperature boron precipitates in form of single crystals with temperature decrease. Experimental products were free from any borides only when Au was used. The maximal length of synthesized B28 crystals was ~100 µm and after their isolation high quality X-ray diffraction data was obtained. Synthesized single crystals of the orthorhombic high-pressure boron phase were studied by means of polarized Raman spectroscopy at ambient conditions. Among all possible 42 Raman-active modes, 32 modes were registered and assigned. Investigation of the high pressure behavior of B28 orthorhombic boron was carried out through combining single crystal X-ray diffraction up to 65 GPa and Raman spectroscopy measurements performed up to 105 GPa. Above 40 GPa discontineous behavior in the mode Grueneisen parameter was detected. At the same pressure an inflection in the dependence of the relative volume of a unit cell versus pressure occurs. However, the structure of the material does not change. It is suggested that B28 undergoes an isostructural phase transformation, probably due to reducing of the polarity of covalent bonds. The orthorhombic B28 boron reveals extraordinary physical properties. Due to very strong covalent bonding it has a very high Vickers hardness HV=58 GPa, making B28 to be the second hardest elemental material after diamond. The electrical resistance and IR-spectroscopic measurements demonstrated the semiconducter nature of B28. Combination of these properties makes the high-pressure boron polymorph a prospective material for industrial applications.

Modeling the exchange of energy and matter within and above a spruce forest with the higher-order closure model ACASA (2010)

Katharina Staudt

Multilayer SVAT-models that contain an advanced turbulence scheme are necessary for the detailed simulation of all relevant exchange processes above and within a forest canopy. The Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) model incorporates such an advanced turbulence scheme, the third-order turbulence closure. This study presents the application of the ACASA model for a spruce forest at the Waldstein-Weidenbrunnen site in the Fichtelgebirge (Germany). The comprehensive micrometeorological and plant physiological measurements performed during the EGER project (ExchanGE processes in mountainous Regions) provided the necessary data base for this purpose, particularly eddy-covariance and sap flux measurements at several heights within the canopy. Thorough model tests were a main focus of this study and led to an improvement of the investigated model. This included both the exploration of the sensitivity and predictive uncertainty of the modeled fluxes and the analysis and correction of model errors that were encountered while working with the model. Furthermore, the ability of the ACASA model to reproduce measured quantities within and above the forest canopy was assessed, with an emphasis on the vertical structure of evapotranspiration and its components. To study the sensitivity and predictive uncertainty of the ACASA model, the Generalized Likelihood Uncertainty Estimation (GLUE) methodology was employed for two five day fair weather periods. Here, the sensitivity of the sensible heat flux, the latent heat flux and the net ecosystem exchange above the forest canopy was assessed. This analysis allowed the identification of influential parameters for the three fluxes. The fluxes were strongly sensitive to only a few parameters while the problem of equifinality was revealed for many parameters. Equifinality is a common problem for complex process-based SVAT-models. The calculated uncertainty bounds showed the ability of the ACASA model to well reproduce the fluxes for two periods with different meteorological conditions. Furthermore, the results of the GLUE analysis indicated weaknesses in the model structure concerning the soil respiration calculations. The latest ACASA version includes multiple improvements in comparison to older model versions which were introduced after a comparison of modeled within- and above-canopy fluxes and turbulence statistics with measurements. The former version of the ACASA model did not explicitly close the energy balance. Rather, an error was included in the model output. This modeled error, however, did not agree with the measured residual at our site and was shown to reach substantial magnitudes depending on the value of the leaf area index. Thus, a method to ensure a closed energy balance for all layers in ACASA was introduced. Measured third-order velocity statistics were largely underestimated by the former ACASA version, which required correcting the calculation algorithms for the third-order moments in the latest ACASA version. Comparisons of third- and second-order velocity statistics showed that simulations of the latest ACASA version were improved but only partly reproduced measurements. Sap flux and eddy-covariance measurements at several heights within the profile provided estimates of all components of evapotranspiration of the forest and its vertical distribution. Canopy transpiration of the stand measured with the eddy-covariance technique delivered larger estimates than measured with the sap flux technique. Possible reasons for this mismatch are discussed, such as a contribution of evaporation from intercepted water that was still present at the beginning of the study period and differences between the eddy-covariance footprint and the area to scale up sap flux measurements. The modeled evapotranspiration components by ACASA compared well to these measurements when taking the uncertainties of these measurements into account. Also, modeled in-canopy profiles of canopy (evapo-) transpiration agreed well with measurements, with a better agreement of mean profiles for daytime, a partly and completely coupled canopy than for nighttime and a decoupled canopy. Largest contributions to canopy (evapo-) transpiration stem from the upper half of the canopy at daytime, whereas during nighttime, the contribution shifted towards lower parts of the canopy. Additionally, model simulations of the 3D model STANDFLUX were included in this study. This study revealed that the ACASA model is a powerful tool to simulate in detail a large range of the relevant exchange processes within and above a spruce forest site. At the same time existing weaknesses in the model code were identified that should be improved in future ACASA versions.

Advection at a forest site – an updated approach (2010)

Lukas Siebicke

The exchange of carbon dioxide (CO2) across the vegetation-atmosphere interface of a spruce forest was investigated. Horizontal and vertical advection are recognized as important terms of the Net Ecosystem Exchange (NEE) budget in addition to the commonly measured turbulent flux and storage flux. Direct advection measurements are challenging because of the instrumental accuracy required to observe small concentration gradients and small wind velocities and because of the spatio-temporal measurement resolution required to observe complex 3-D flow phenomena. This work presents an experimental multi-analyzer setup for the observation of horizontal CO2 concentration gradients with high temporal resolution and good spatial resolution with no tradeoff between the two. A statistical approach was developed to correct for inter-instrument bias by applying a conditional time dependent bias correction. This approach relies on properties of probability density distributions of concentration differences between one sample point and the spatial average of the sample point field. Sub-canopy CO2 concentration gradients observed with the above presented system showed a high spatial variability which was dependent on vegetation structure. Local concentration perturbations correlated with statistical properties of coherent structures and were explained by vertical exchange between CO2 enriched sub-canopy air and low concentration above-canopy air. The small-scale variability of CO2 concentration gradients brings into question the representativity of horizontal advection measurements for the control volume if observed with a low spatial resolution. Vertical advection estimates rely on accurate measurements of vertical wind velocity (w). Different procedures were applied during coordinate rotation to align the coordinate system of the sonic anemometer with the long-term stream lines. Spatial variability of the wind field was addressed by a sector-wise coordinate rotation. An investigation of temporal aspects of vertical wind velocity showed significant contributions from low frequencies in the spectrum of w. The impact of the data set length used for coordinate rotation on w and on vertical advection was investigated and observed to be large. A sequential coordinate rotation with controlled window length was proposed. Advection contributed significantly to NEE during the night and during transition periods at the Waldstein-Weidenbrunnen (DE-Bay) FLUXNET site. Daily NEE budgets were more realistic, compared to NEE from turbulent flux and storage change alone, if direct advection measurements from continuous and bias corrected gradient sampling were included, reducing the estimated daily carbon sequestration of the forest by almost 50 %.

Water flow paths in soils of an undisturbed and landslide affected mature montane rainforest in South Ecuador (2010)

Folkert Christian Bauer

The number of previous hydrological studies concerning water flow paths in tropical montane rainforest is small. However, due to the increasing pressure of deforestation and land use change comprehensive knowledge of these natural ecosystems is needed if sustainable land use strategies should keep negative effects of human impacts on water flow paths as low as possible. In this context, present work addresses the identification, characterisation, and modelling of water flow paths in soils of an undisturbed and landslide affected natural Andean forest ecosystem in the south of Ecuador whose deforestation rate is one of the highest in South America. In an investigation area situated in the Andes of South Ecuador, in gentler slopes and altitudes above 2100 m ASL mainly Stagnosols and Histosols with stagnic colour pattern and low to negligible rock fragment content prevail. With increasing altitude the abundance of these soils increase, while the presence of Cambisols and Regosols is most pronounced below 2100 m ASL and clearly correlated with the slope angle. Therefore, these soils were mainly encountered in steeper, particularly landslide affected sites often resembling a melange of fine soil and high contents of rock fragments. Aside the investigation of the influence of the rock fragment content on soil hydrological- and physical parameters such as the relationship between rock fragment content and saturated hydraulic conductivity of the soil, present study aims particularly to investigate flow paths of water in soils of landslide affected and unaffected hillslopes. Therefore, we employed conventional field- and laboratory methods, dye tracer experiments including an appropriate image processing technique, as well as statistical models. Results show that both rock fragment content and bulk density control significantly, but not largely the saturated hydraulic conductivity of the mineral soils. Dye tracer experiments and soil parameters document a deeper percolation in the landslide affected hillslopes than in the landslide unaffected hillslopes, where we found preferential flow in root channels with low soil matrix interaction as dominant flow mechanism. A surface near quasi impervious layer along the interface between topsoil and subsoil limits percolation of the water giving the prerequisites of a lateral shallow subsurface flow along the interface between topsoil and organic layer. This is in line with previous studies performed in the same investigation area which already proved indirectly the existence of this flow. However, in none of these studies the shallow subsurface flow was assigned to certain slope inclinations or altitudes. Due to a recently published digital soil map and the results we obtained from the landslide unaffected sites, we know that particularly in hillslopes of less than 30 degrees above 2100 m ASL prerequisites are given for spatially extended shallow subsurface flow. However, even if these prerequisites are not evident for the landslide affected hillslopes, we cannot exclude the possibility of shallow subsurface flow occurrence here since soil cover of the steep terrain is relatively shallow while rainfall is high throughout the year. Therefore, and given that key parameters such as permeability of subsoil and bedrock, interception and evaporation remain unclear or were investigated exclusively such as the spatial variability of the saturated hydraulic conductivity, we conducted a series of virtual experiments in order to assess the potential occurrence of shallow subsurface flow in Cambisols below 2100 m ASL. In these experiments we also included the organic layer being highly abundant in the investigation area, whose hydraulic parameters were estimated by means of inverse numerical modelling. The virtual experiments were based on a two dimensional finite element model representing a steep forested hillslope transect of approx. 54 m length. Aside soil properties, evapotranspiration and interception, the model included the spatial variability of the saturated hydraulic conductivity, the pressure head and their spatial trends. The results of virtual experiment series show that a sound evidence of the key parameters aforementioned is obligate if process conceptualisation regarding shallow subsurface flow generation, but also landslide initiation, solute and matter transport is in the spotlight.

Characterization of reactive and non reactive trace gas fluxes in and above soil (2010)

Anika Bargsten

Nitrogen is one of the most important compounds on earth. All organisms need nitrogen to live and grow. Even the majority (78.08%) of the atmosphere (and so the air we breathe) is dinitrogen. Over the last century, human activities have dramatically increased emissions and removal of nitrogen to the global atmosphere by as much as three to five fold. Nitrous oxide is the fourth largest single contributor to positive radiative forcing, and serves as the only long-lived atmospheric tracer of human perturbations of the global nitrogen cycle. Nitrogen oxides belong to the so called indirect greenhouse gases. These indirect greenhouse gases control the abundances of direct greenhouse gases through atmospheric chemistry and contribute on this way to the greenhouse effect. For a better understanding of these feedback mechanisms it is necessary to know the source strength of nitric oxide and nitrous oxide. Thus, the knowledge about exchange processes of nitrogen is of interest and importance for scientist and policy makers, likewise. This thesis contributes the understanding of processes in the nitrogen cycle. The thesis is addressed on nitric and nitrous oxide emissions. Nitric oxide emissions were measured on soil samples using an automated laboratory system. Nitrous oxide emissions were measured directly on the field site using a closed chamber technique. The laboratory measurements were compared with field measurements of NO (modified Bowen ratio method) at a grass land site. The field NO fluxes were always around 1.8 ng m 2 s-1 while the laboratory derived NO fluxes were between 2.1 and 5,2 ng m-2 s-1. The agreement between the two data sets is considered to be quite good. The laboratory derived NO fluxes exceeded the field NO fluxes by a factor of 1.5 to 2.5. Most studies of nitric oxide (NO) emission potentials up to now have investigated mineral soil layers only. In this thesis soil organic matter was sampled for laboratory measurements under different understory types (moss, grass, spruce, blueberries) in a humid mountainous Norway spruce forest plantation in the Fichtelgebirge (Germany). In this thesis the response of net potential NO fluxes on physical and chemical soil conditions (water content and temperature, bulk density, particle density, pH, C/N ratio, organic C, soil ammonium, soil nitrate) was determined. Net potential NO fluxes (in terms of mass of N) from soil samples taken under the different understories ranged from 1.7 - 9.8 ng m 2 s-1 (soil sampled under grass and moss cover), 55.4 - 59.3 ng m-2 s-1 (soil sampled under spruce cover), and 43.7 - 114.6 ng m 2 s-1 (soil sampled under blueberry cover) at optimum water content and a soil temperature of 10°C. Effects of soil physical and chemical characteristics on the net potential NO flux were statistically significant (0.01 probability level) only for NH4+. Therefore, as an alternative explanation for the differences in soil biogenic NO emission we consider more biological factors like understory vegetation type, amount of roots, and degree of mycorrhization; they provide a potential explanation of the observed differences of net potential NO fluxes. Also, soil nitrous oxide (N2O) emissions in an unmanaged, old growth beech forest in the Hainich National Park, Germany, were measured at 15 plots over a one-year period (November 2005 to November 2006). The annual field N2O flux rate was 0.46±0.32 kg ha 1 yr 1. The N2O emissions showed a background emission pattern with two event based N2O peaks. A correlation analysis showed that the distance between plots (up to 380 m) was secondary for their flux correlations. Annual N2O fluxes obtained from a standard model (Forest-DNDC) parameterized with soil parameters as well as daily temperature and precipitation substantially overestimated the actual field N2O fluxes and also did not describe their actual temporal and spatial variabilities. Temporal variability was described well by the model only at plots with higher soil organic carbon and the modelled N2O fluxes increased during freezing periods only were soil organic carbon was larger than 0.06 kg-1 C kg. The results indicate that the natural background of nitrous oxide emissions may be lower than previously thought and also lower than assumed in standard modelling. This suggests a higher anthropogenic contribution to N2O emissions.

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